Ohmic contact configuration

ABSTRACT

A contact configuration has an ohmic contact between a metalization layer and a semiconductor body of monocrystalline semiconductor material. An amorphous semiconductor layer is formed between the metalization layer and the monocrystalline semiconductor body. The layer is formed of the same semiconductor material as the body. The contact configuration is either produced by applying amorphous semiconductor material on the semiconductor body (e.g., sputtering, vapor deposition, glow discharge) or by damage formation in the semiconductor body.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention lies in the semiconductor technology field.More specifically, the invention relates to a contact configuration withan ohmic contact between a metalization layer and a semiconductor bodymade of a monocrystalline semiconductor material.

[0003] In order to produce an ohmic contact between a metalization layerand a semiconductor body, a sufficiently high doping concentration isrequired in the semiconductor material of the semiconductor body. By wayof example, if the metalization layer comprises aluminum and thesemiconductor body comprises p-doped silicon, then the dopingconcentration in the surface region of the semiconductor body withrespect to the metalization layer should be at least 10¹⁷ doping atomscm⁻³. If the silicon of the semiconductor body is n-doped, then asurface doping concentration of even in excess of 10¹⁹ dopant atoms cm⁻³is required.

[0004] These minimum doping concentrations pose a problem if the regionsof the semiconductor body that adjoin the contact region with respect tothe metalization layer are not intended to have a high emitterefficiency. This is because the injection behavior of an emitter dependscrucially on the dopant dose introduced into its region. In asemiconductor body, however, even with a deposition very near thesurface for example by way of ion implantation and a subsequentannealing step, high surface doping concentrations cannot be producedwith arbitrarily small dopant doses of the order of magnitude of lessthan 10¹³ dopant atoms cm⁻², for example, without significantredistribution.

[0005] At the present time, the contact to the body zone in powerMOSFETs and IGBTs (insulated gate bipolar transistor) is preferablyconnected to the source electrode by a heavily doped p-conducting regionwith the lowest possible resistance in order that the pn junctionbetween body zone and source zone is not forward-biased with respect tothe source zone in the event of a high shunt current. For this wouldlead to a so-called “latch-up” of the power MOSFET or IGBT, whichprevents controllability via the gate and brings about destruction ofthe power MOSFET or IGBT in the absence of external additional measures.

[0006] The body diode thus integrated between body zone and source zonehas the effect, in a power MOSFET or IGBT, that the latter is veryheavily flooded with charge carriers in the reverse direction. Thecommutation properties of the body diode are very poor due to the highp-type doping of the body zone on the front side of the power MOSFET. Bycontrast, IGBTs exhibit a certain reverse blocking capability due to therear-side pn junction with respect to the collector zone. Here, the IGBTis already flooded with charge carriers in normal forward operation,which charge carriers then have to be depleted in the event oftransition to the blocking state. The resultant charge carrier currentto the cell then has to be conducted away with a sufficiently lowresistance via the p-conducting body zone to the body contact.

[0007] It is quite generally the case with bipolar transistors anddiodes that a relatively high doping of the regions in the vicinity ofthe metalization layer with which contact is to be made leads to anoften undesirably strong emitter, which results in a correspondinglyhigh degree of flooding of the component with charge carriers and thusin higher switching losses.

[0008] In the prior art, the use of power MOSFETs in group circuits inparticular at relatively high voltages of above about 300 V has beenpossible only to a very limited extent. At relatively low voltages ofbelow 300 V, the switching losses in such power MOSFETs are relativelyhigh. At the present time, the required latch-up strength of powerMOSFETs or IGBTs is ensured through precise design of their cells andcomplicated fabrication methods.

[0009] In the case of bipolar transistors and diodes, low emitterefficiencies can be ensured on the one hand through correspondingly lowdopant doses and on the other hand through optimized doping methods.Reference is had, in this context, to the commonly assigned publishedapplication U.S. Ser. No. 2003/0122151 A1 and German published patentapplication DE 100 31 461 A1, for example, which describe a high-voltagediode wherein the doping concentrations of an anode region and of acathode region are optimized with regard to the basic functions of“static blocking” and “forward state.” However, all of these measuresare usually insufficient for achieving a weak emitter that is desired inmany cases.

[0010] For this reason, it is necessary to employ additional methods bywhich a subsequent weakening of the emitter efficiency is achieved bymeans of local or homogeneous setting of the charge carrier lifetime.What is particularly of significance here is a lowering of the chargecarrier lifetime through local damage of the semiconductor crystallattice in or in the vicinity of the emitter by irradiation withhigh-energy particles such as, for example, electrons, protons or heliumatoms. What is disadvantageous about such a procedure, however, is onceagain the susceptibility of completed components to process variations.

SUMMARY OF THE INVENTION

[0011] It is accordingly an object of the invention to provide an ohmiccontact configuration, which overcomes the above-mentioned disadvantagesof the heretofore-known devices and methods of this general type andspecifies a configuration with an ohmic contact between a metalizationlayer and a semiconductor body that can be produced in a simple mannerand is able to ensure a low emitter efficiency. Moreover, the intentionis to provide an advantageous method for producing such a contactconfiguration.

[0012] With the foregoing and other objects in view there is provided,in accordance with the invention, a contact configuration, comprising:

[0013] a semiconductor body of semiconductor material in amonocrystalline phase;

[0014] a metalization layer; and

[0015] a layer of said semiconductor material in a substantiallyamorphous phase disposed between said semiconductor body and saidmetalization layer, for forming an ohmic contact between saidmetalization layer and said semiconductor body.

[0016] In other words, a contact configuration of the type mentioned inthe introduction is provided with a layer made of the amorphoussemiconductor material of the semiconductor body, the layer beingprovided between the semiconductor body and the metalization layer.

[0017] The invention is thus based on the completely novel insightconcerning the usability of amorphous silicon: previously, amorphoussilicon has been used for anti-reflection layers and for passivation.The invention now envisages that amorphous silicon may serve, this beingcompletely novel, as a contact material between a metalization layer anda semiconductor body comprising silicon.

[0018] However, the invention is not restricted to silicon: rather, itcan generally also be applied to other semiconductor materials, such as,for example, to silicon carbide, compound semiconductors etc. Thus, byway of example, an amorphous silicon carbide layer can effect an ohmiccontact between a metalization layer and a silicon carbide semiconductorbody.

[0019] The contact configuration according to the invention thus enablesan ohmic junction between, in particular, a lightly doped siliconsemiconductor body and a metalization layer applied thereto by anintermediate layer made of amorphous silicon being deposited onto thesilicon of the semiconductor body. On account of its high defectdensity, amorphous silicon has the desired property of forming an ohmiccontact between the amorphous silicon layer, on the one hand, and themetalization layer deposited thereon, on the other, as well as betweenthe amorphous silicon layer on the one hand, and the crystalline siliconof the semiconductor body on the other hand. This specifically holdstrue even when the preferably n-conducting doping in the amorphoussilicon layer is present only in a low concentration.

[0020] Amorphous silicon vapor-deposited or sputtered onto a siliconsemiconductor body is generally n-conducting after a heat treatmentwhich follows its deposition, which heat treatment may preferablyproceed at about 350° C. to 450° C. In this case, the amorphous siliconmay already contain a relatively high concentration of hydrogen,depending on its production process. Since the sheet resistance thatresults in an amorphous silicon layer is relatively high, it may beexpedient for hydrogen atoms additionally to be incorporated into theamorphous silicon layer in order to increase the n-type doping in atargeted manner.

[0021] The incorporation of the hydrogen atoms into the amorphoussilicon layer may be effected for example by the heat treatment whichfollows the deposition, and which is carried at about 350° C. to 450°C., being performed in a hydrogen-containing atmosphere. A furtherpossibility consists in producing the amorphous silicon layer by meansof a glow discharge process in a silane atmosphere (SiH₄ atmosphere) orelse in carrying out the sputtering process itself in ahydrogen-containing atmosphere.

[0022] A primary advantage of the contact configuration according to theinvention is that it enables an ohmic contact on an n-doped or elsep-doped semiconductor body, and in particular on a silicon semiconductorbody, without the need for the contact to have a high emitterefficiency, since the emitter efficiency remains low due to theamorphous structure of the deposited layer.

[0023] In addition to or instead of the doping by means of hydrogen, itis also possible to provide an amorphous silicon layer with othern-doping substances, such as phosphorus, for example. Such an additionaldoping is preferably performed since hydrogen-doped silicon can beelectrically actively doped more easily with phosphorus, for example, orelse—for the case of a targeted p-doping—with boron, for example.

[0024] The contact configuration according to the invention isadvantageously employed for example for the source contact of a MOScomponent, that is to say of a MOSFET or IGBT, for example. In the caseof such a MOSFET component, it is possible to dispense with a shortcircuit between body zone and source zone owing to the poor emitterefficiency. In this case, n-doped amorphous silicon can be depositedeither directly on a p-doped semiconductor body (bulk) as source zone orchannel terminal or on a more weakly n-doped source zone as contactmaterial.

[0025] If such an n-doped emitter is employed for diode structures, thenthe possibility of producing defects in the depth of the siliconsemiconductor body through an additional irradiation by means of protonsor helium atoms is also afforded, which defects may be provided withhydrogen during the above-described heat treatment process and then formdonors. This process can thus be used to form an upstream field stopzone which is desired for many diode structures and, inter alia, leadsto a softer switch-off (this will be discussed in more detail furtherbelow in connection with FIG. 1). This zone may also lead to a targetedraising of the emitter efficiency. However, it is also possible toprovide a raising of the emitter efficiency of that semiconductor regionof the semiconductor body which is coated with amorphous silicon throughan additional moderate conventional doping of the crystalline siliconregion situated in direct proximity to the amorphous silicon layer, forexample by means of phosphorus atoms in the case of an n-type doping andfor example by means of boron atoms in the case of a p-type doping.

[0026] In principle, it is also possible to use the contactconfiguration according to the invention to produce a stable ohmiccontact on a lightly doped p-conducting region for an IGBT, for example.This contact is likewise distinguished by a low emitter efficiency. Inthis case, the amorphous silicon may also be produced in p-conductingfashion through suitable doping. In this case, too, the emitterefficiency may easily be raised as required through a moderateadditional doping of the region of the crystalline silicon which issituated in the region of the interface with the amorphous siliconlayer. Thus, in IGBTs for relatively high switching frequencies, at thepresent time preferably weak p-conducting emitters are used for reducingthe switch-off losses. The use of amorphous silicon as contact materialin this case makes it possible to further reduce the p-type dose andthus the switching losses. At the present time, the minimum emitterefficiency is limited here by the ohmic contact-connectability.

[0027] The contact configuration according to the invention makes itpossible to protect specific regions in components which become very hoton account of instances of current splitting by the efficiency of an n-or p-conducting emitter formed by an amorphous silicon layer beinglocally attenuated in the critical component regions. Such an amorphoussilicon layer can be produced in a self-aligning manner by exploitingthe effect that amorphous silicon starts to recrystallize attemperatures in the range above 600° C., which increases the contactresistance. Thus, if the component is operated above a noncriticalcurrent density range over a certain period of time, then the injectioncan also be locally attenuated on account of the local temperatureincrease and the locally increased contact resistance resultingtherefrom. This reduces the injection of such an emitter in the criticalcomponent regions, that is to say for example in the edge region ofdiodes during dynamic operation or, in pressure contact IGBTs, in theregion situated below the edge of the pressure piece. This leads to aload relief during switch-off in the edge region in the case of thediodes, for example.

[0028] In an advantageous manner, in the case of a contact configurationwith a hydrogen-containing and generally additionally doped siliconlayer, an outdiffusion of hydrogen atoms, which already occurs to anappreciable extent at temperatures in the region of 400° C., alreadysuffices to impair the injection behavior of the emitter in locallytargeted fashion. An alternative without utilizing this effect islocally reducing the emitter efficiency by locally driving out thedoping from the amorphous silicon by means of a locally delimited inputof heat from outside. Such an input of heat may be effected for exampleby means of a heated grid or through radiation which acts locally, suchas laser radiation for example, or is locally shielded, which can bedone for example by means of a screen in an RTA furnace (RTA=RapidThermal Annealing). It is also possible to allow the radiation to act inpulsed fashion.

[0029] The contact configuration according to the invention may beproduced by deposition by means of vapor deposition or sputtering ofamorphous semiconductor material, such as, in particular, silicon orsilicon carbide. However, it is also possible not to deposit theamorphous semiconductor material but rather to amorphize the surface ofmonocrystalline semiconductor material. With silicon, then, no amorphoussilicon is deposited in this case. Rather, monocrystalline silicon issubjected to a damage process in order to amorphize it in regions wherethe intention is to create a contact configuration with an ohmiccontact.

[0030] It is advantageous, particularly for contact configurations onthe rear side of a semiconductor wafer, to produce a damage by means ofan implantation with a non-doping element. With this procedure, theactual emitter is then implanted particularly shallowly, so thatpractically all of the implanted atoms remain in the region of thedamage. As an alternative, there may be a low dose of this emitter inthe crystalline region as well, wherein case this dose should be so lowthat the targeted weak emitter efficiency is not exceeded. Elements ofthe third period of the periodic table, such as silicon or argon, forexample, are preferably suitable for a damage implantation. Theseelements have a relatively low amorphization dose in the region of5·10¹⁴ cm⁻² and, on the other hand, have significantly greaterpenetration depths than elements of the fourth period of the periodictable.

[0031] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0032] Although the invention is illustrated and described herein asembodied in an ohmic contact configuration, it is nevertheless notintended to be limited to the details shown, since various modificationsand structural changes may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

[0033] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a graph plotting a fundamental doping profile of a 1200V diode, with the doping plotted as a function of an anode distance;

[0035]FIG. 2 is a diagrammatic sectional illustration through a contactconfiguration according to the invention;

[0036]FIG. 3 is a sectional view of a trench component with the contactconfiguration according to the invention; and

[0037]FIG. 4 is a sectional view of a planar component with the contactconfiguration according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a fundamental dopingprofile of a 1200 V diode with the contact configuration according tothe invention. In this case, the basic doping BD in charge carriers/cm³is plotted as a function of a distance d from the anode of the diode inμm. In the case of this diode, a rear-side contact comprises amorphoussilicon (a-Si) and has a basic doping of between 10¹³ and 10¹⁴ chargecarriers cm⁻³. The doping profile firstly exhibits a region with ahomogeneous basic doping, followed by a field stop zone with a highdoping. This field stop zone then undergoes transition to a layer madeof amorphous silicon on the rear side of the diode.

[0039] The field stop zone may be produced for example through anadditional irradiation by means of protons or helium atoms. The protonsor helium atoms produce defects in the depth of the semiconductor body,which defects are provided with hydrogen during a heat treatment processafter the deposition of the amorphous silicon layer and form donors.Whereas the hydrogen is already present in the semiconductor body in thecase of proton implantation, in the case of prior helium implantation itfirst has to be indiffused for example from the vapor phase or a plasma.The donors increase the doping in the region of the field stop zoneabove the homogeneous basic doping. The field stop zone has theadvantage that it ensures, inter alia, a softer switch-off of the diode.

[0040]FIG. 2 shows a diagrammatic sectional illustration through thecontact configuration according to the invention. An amorphoussemiconductor layer 2 is disposed on a semiconductor body 1 made ofmonocrystalline silicon or monocrystalline silicon carbide, for example.The amorphous semiconductor layer 2 is likewise made of silicon orsilicon carbide. The layer thickness of the layer 2 is in the nm rangeand may, for example, lie between 2 nm and 100 nm or a few 100 nm. Thedoping concentration in the layer 2 is relatively low and, for example,lies between 10¹⁵ and 10¹⁶ charge carriers cm⁻³.

[0041] A metalization layer 3 is applied as contact on the layer 2. Byway of example, aluminum or chromium or aluminum/chromium may be usedfor the metalization layer 3.

[0042]FIG. 3 shows, as a concrete exemplary embodiment of the contactconfiguration according to the invention, a sectional illustrationthrough a vertical trench MOSFET with an n-doped silicon semiconductorbody 1 into which are introduced trenches 4 filled with polycrystallinesilicon as gate electrode. A p-doped body zone 5 is situated in thesemiconductor body 1, at the top side thereof, an n-doped source zone 6being provided in turn at the top side of the body zone. The source zone6 and the body zone 5 are contact-connected by a metalization layer 3made of aluminum.

[0043] An n⁺-doped terminal zone 7 is additionally provided on the rearside of the semiconductor body 1. A drain contact 8 (D) is provided onthe terminal zone.

[0044] According to the invention, the body zone 5 and the source zone6, on the one hand, and/or the n⁺-conducting contact zone 7 are nowprovided with a p-doped or n-doped layer 2 made of amorphous silicon.The layer 2 may be produced by vapor deposition, as has been explainedabove, or else by amorphization.

[0045]FIG. 4 shows, as a further exemplary embodiment of the contactconfiguration according to the invention, a sectional illustrationthrough a planar IGBT with an n⁻-conducting silicon semiconductor body1, an additional lightly doped p-conducting collector layer 9, acollector contact layer 10 (K), p-conducting body zones 5, lightly dopedn-conducting source zone 6, gate electrodes 11 in an insulating layer 13made of silicon dioxide with a gate oxide 12 and an aluminummetalization layer 3.

[0046] Generally, the layer 9 may act as an emitter and be doped soweakly that, without the amorphous layer 2, a Schottky contact or anohmic contact with a relatively high contact resistance would beproduced.

[0047] According to the invention, layers 2 made of amorphous dopedsilicon are provided below the aluminum metalization 3 in the body zone5 and the source zone 6 and/or between the p-conducting collector layer9 and the collector contact layer 10 made likewise of aluminum, in orderto enable a relatively low or even negligible doping of the zone 6and/or of the layer 9. The layers 2 may be n-doped in the region of thesource zone 6 and body zone 5 and be p-doped in the region of thecollector layer 9. It goes without saying that respectively oppositeconduction types are possible for the doping in this case as well.

[0048] The layers 2 may be produced by deposition by means of vapordeposition or sputtering in an optionally hydrogen-containingatmosphere, which may be followed by a heat treatment at about 350° C.to 450° C. in likewise a hydrogen-containing atmosphere. However, it isalso possible to produce the amorphous layer 2 by means of a glowdischarge process in an SiH₄ atmosphere. Finally, the amorphous layerneed not actually be deposited: rather, it is possible to amorphize thesurface of the semiconductor body 1 itself (cf. FIG. 2) by introducing adamage by means of implantation with a non-doping element, such as, inparticular, an element of the third period of the periodic table, thatis to say silicon or argon, for example. This implantation may beeffected with a dose of about 5·10¹⁴ to 1·10¹⁶ cm⁻².

[0049] The layer 2 may, preferably, also be locally recrystallized incomponent regions. This recrystallization may be performed attemperatures in excess of about 600° C. Regions which are suitable for arecrystallization are those regions wherein the emitter efficiency isintended to be reduced compared with the rest of the emitter area.

We claim:
 1. A contact configuration, comprising: a semiconductor bodyof semiconductor material in a monocrystalline phase; a metalizationlayer; and a layer of said semiconductor material in a substantiallyamorphous phase disposed between said semiconductor body and saidmetalization layer, for forming an ohmic contact between saidmetalization layer and said semiconductor body.
 2. The contactconfiguration according to claim 1, wherein said semiconductor materialis silicon.
 3. The contact configuration according to claim 2, whereinsaid layer is a layer of amorphous silicon doped with hydrogen.
 4. Thecontact configuration according to claim 2, wherein said layer is alayer of amorphous silicon with oxygen atoms incorporated therein. 5.The contact configuration according to claim 2, wherein said siliconsemiconductor body is n-conducting in a region of said layer ofamorphous silicon.
 6. The contact configuration according to claim 2,wherein said layer is a layer of amorphous silicon additionally dopedwith phosphorus.
 7. The contact configuration according to claim 2,wherein said layer is a layer of amorphous silicon doped with boron. 8.The contact configuration according to claim 2, wherein said siliconsemiconductor body is p-conducting in a region of said layer ofamorphous silicon.
 9. The contact configuration according to claim 1,wherein said layer of amorphous semiconductor material has a thicknessin the order of magnitude of nanometers.
 10. The contact configurationaccording to claim 9, wherein said thickness of said layer lies between2 and 100 nm.
 11. The contact configuration according to claim 1,wherein said layer of amorphous semiconductor material has a doping ofbetween 10¹⁵ and 10¹⁶ charge carriers per cm³.
 12. The contactconfiguration according to claim 1, wherein said metalization layer isformed of a metal selected from the group consisting of aluminum,chromium, and aluminum/chromium.
 13. The contact configuration accordingto claim 1, which comprises one of a trench component and a planarcomponent formed in said semiconductor body.
 14. The contactconfiguration according to claim 13, wherein said component is selectedfrom the group consisting of a diode, a bipolar transistor, a MOSFET,and an IGBT.
 15. The contact configuration according to claim 1, whichcomprises a field stop zone in said semiconductor body, said field stopzone adjoining said layer of said amorphous semiconductor material. 16.The contact configuration according to claim 1, which further comprisesan additional layer in said semiconductor body in a region of said layerof amorphous semiconductor material, said additional layer forming anemitter.
 17. The contact configuration according to claim 16, whereinsaid additional layer and said semiconductor body are of a commonconductivity type.
 18. The contact configuration according to claim 16,wherein said additional layer and said semiconductor body havingmutually opposite conductivity types.
 19. The contact configurationaccording to claim 16, wherein said additional layer is doped so weaklythat, without said layer of amorphous semiconductor material, saidadditional layer forms one of a Schottky contact or an ohmic contactwith a relatively high contact resistance.
 20. The contact configurationaccording to claim 1, wherein said layer of amorphous semiconductormaterial is formed on at least one of a front side and a rear side ofsaid semiconductor body.
 21. The contact configuration according toclaim 20, wherein said layer of amorphous semiconductor material isformed to locally attenuate an injection of charge carriers in criticalcomponent regions.
 22. The contact configuration according to claim 1,wherein said layer of amorphous semiconductor material is locallyrecrystallized.
 23. The contact configuration according to claim 1,wherein in said amorphous semiconductor material is silicon carbide. 24.A method for producing the contact configuration according to claim 1which comprises: providing a semiconductor body; applying amorphoussemiconductor material on the semiconductor body by a process selectedfrom the group consisting of sputtering, vapor deposition, and glowdischarge; and subsequently subjecting the amorphous semiconductormaterial to heat treatment and forming the contact configurationaccording to claim
 1. 25. The method according to claim 24, whichcomprises performing the heat treatment at about 350° C. to 450° C. 26.The method according to claim 24, which comprises sputtering in ahydrogen-containing atmosphere.
 27. The method according to claim 24,which comprises performing the heat treatment in a hydrogen-containingatmosphere.
 28. The method according to claim 24, which compriseslocally recrystallizing the amorphous layer of silicon at temperaturesabove about 600° C. in component regions.
 29. A method for producing thecontact configuration according to claim 1 which comprises: providing asemiconductor body; and forming an amorphous semiconductor material inthe semiconductor body by damage formation, and producing the contactconfiguration according to claim
 1. 30. The method according to claim29, which comprises doping the amorphous semiconductor material.
 31. Themethod according to claim 29, wherein the amorphous semiconductormaterial is doped with a material selected from the group consisting ofboron and phosphorous.
 32. The method according to claim 29, whichcomprises introducing an additional layer into the semiconductor body ina region of a layer formed of amorphous semiconductor material.
 33. Themethod according to claim 32, wherein the additional layer is weaklydoped.
 34. The method according to claim 29, wherein the damageformation is effected by implantation.
 35. The method according to claim34, wherein the implantation comprises implanting elements of the thirdperiod of the periodic table of elements.
 36. The method according toclaim 34, which comprises implanting with an implantation dose of about5·10¹⁴ cm⁻² to 1·10¹⁶ cm⁻².
 37. The method according to claim 29, whichcomprises locally recrystallizing the amorphous layer of silicon attemperatures above about 600° C. in component regions.